Only a few companies with GTX 580 Waterblocks have backward compatibility with GTX 570 and EK would be one. I have heared that they are not going to manufacture any GTX 570 waterblocks as GTX 580 has the same reference pcb design.

All water blocks perform pretty much the same, just flow rates and maybe different VRM cooling... there arn't any roundups for GTX 580 blocks yet (since its very time consuming and damaging to the card)... but you can go to skineelabs and look at his GTX 480 waterblock round up... since there wasnt much change from GTX 480 to GTX 580 you can probably use the same charts to determine which waterblock you want.

I got the Koolance one :-).. I was going to with EK... but they took awhile to release a nickle/acetal waterblock.. but hey nothing wrong with Koolance.. plus I think they look a tad better.

Backplate will only improve aesthetics of the GPU.. no performance increase.

My GPU never reached over 56 degrees and it's overclocked to the max at the moment.. room ambients of 28-29 degrees.